The present invention relates to tree shear heads capable of accumulating a plurality of cut trees and more specifically relates to improvements in shear heads of the type disclosed in U.S. Pat. No. 3,862,652 granted to Johnson on Jan. 28, 1975.
The tree shear head disclosed in the above-identified Johnson patent includes a main upright frame to which a pair of laterally spaced grapple tongs are pivotally mounted for movement between open and closed positions for selectively gripping trees against the frame and releasing sheared trees from the shear head. The tongs are selectively moved by hydraulic actuators which are connected in parallel with each other and to a control valve such as to be concurrently opened and closed. Thus, the tongs are not adapted to be used to accumulate trees one-by-one in the shear head as might be desired when working in thick stands of trees which are relatively small in diameter.
Tree shear heads having accumulating ability are known in the art. An example of such a tree shear head is disclosed in U.S. Pat. No. 3,910,326 granted to Tucek on Oct. 7, 1975. The shear head disclosed in the Tucek patent is somewhat similar to that disclosed in the above-mentioned Johnson patent to the extent that it has a pair of grapple tongs selectively opened and closed by respective actuators connected in parallel for concurrent controlled actuation by means of one direction control valve. However, the Tucek design additionally includes an accumulator tong, an actuator for this tong and additional circuitry for controlling the accumulator tong actuator. This additional circuitry is connected to the lines for conveying pressure and exhaust fuild to and from the grapple tong actuators and includes a set of four check valves which operate to route fluid to and from a solenoid-operated, two-position, four-way valve coupled to the accumulator tong actuator such that when the last-mentioned valve is in a normal de-activiated position, the actuator will act to maintain the accumulator tong in a closed position during both opening and closing of the grapple tongs. This is the mode of operation of the shear head when trees are not being accumulated. When it is desired to accumulate sheared trees, the solenoid-operated valve is momentarily energized such that the flow of fluid to the accumulator tong actuator is momentarily reversed to effect cycling of the accumulator tong from a closed position behind a tree just sheared to a closed position against a forward portion of the tree.
While the Tucek design teaches how a pre-existing shear head having no accumulating capabilities may be modified to have such capabilities, the manner chosen is not compatible with the aforementioned Johnson shear head since the latter is considerably more vertically compact than is the Tucek shear head and has no room for an additional tong to be mounted on the frame thereof.